Active and passive devices employing optical waveguide structures for use in communication applications are well known in the art. Integrated optical structures involve the monolithic integration of one or more optical waveguide structures on a common substrate. Optical waveguide structures include modulators and switches that typically use laser diode optical sources and that transmit light (i.e., an optical signal) along an optical fiber. An example of a passive structure is a fixed optical power splitter, while an example of an active structure is an optical switch.
A single substrate may include a plurality of optical waveguide structures and integrated optical directional couplers. An integrated optical directional coupler is formed when two optical waveguides are situated such that their evanescent mode fields overlap. The distance between the two waveguides is decreased by using curved waveguides, such as “C-shaped” waveguides, that have symmetric bends, whereby each of the waveguides “bends” toward the other. The two waveguides are used to confine and guide the optical signal from an input port to an output port.
A typical configuration of an optical directional coupler has two input ports and two output ports. In this manner, light can be guided from either of the two input ports to either of the two output ports. The directional coupler can operate as a straight through switch or as a cross-over switch. When the directional coupler is activated, the selected input port and the selected output port are “coupled” so that the light received at the input port is routed to the appropriate output port.
Many applications have a requirement for a high gain optical amplifier or Q switched laser that can sustain high power pulses of short duration. In order to meet this requirement, an optical switch with very low optical throughput loss during the “on” pulse is needed.
In a conventional directional coupler acting as an optical switch, light is lost due to the bend in the waveguides. Optical loss can be high even when the directional coupler acts as a straight through switch. Typical throughput loss is between three to four dB, and can be even higher.
A low loss integrated optical switch is thus needed which overcomes one or more of the shortcomings of the prior art.